Groups > linux.kernel > #1319845

Re: [PATCH] signals: work around random wakeups in sigsuspend()

From	Oleg Nesterov <oleg@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] signals: work around random wakeups in sigsuspend()
Date	2016-01-27 22:10 +0100
Message-ID	<qVFvL-1dk-73@gated-at.bofh.it> (permalink)
References	(1 earlier) <qUX1F-1E8-13@gated-at.bofh.it> <qVjbR-1GJ-29@gated-at.bofh.it> <qVtXz-Pn-11@gated-at.bofh.it> <qVBs7-6oZ-43@gated-at.bofh.it> <qVDaA-7NJ-75@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 01/27, Andrew Morton wrote:
>
> On Wed, 27 Jan 2016 17:41:54 +0100 Oleg Nesterov <oleg@redhat.com> wrote:
>
> > IOW, signal_pending() is the "special" condition, you do not need to serialize
> > this check with task->state setting, exactly because schedule() knows about the
> > signals.
>
> So it's non-buggy because signal_pending() is special.  But it *looks*
> buggy!  And there's no comment there explaining why it looks buggy but
> isn't, so someone may later come along and "fix" it for us.

perhaps we can add a comment somewhere in sched.h to explain that a task can
never sleep with task->state == STATE if signal_pending_state(STATE) is true.

Every user of signal_pending() in the wait-event-like loop relies on this well-
known fact. Say, wait_event_interruptible() or __mutex_lock_common().

This is actually more about task->state, not about TIF_SIGPENDING imo.

Oleg.

Thread

[PATCH] signals: work around random wakeups in sigsuspend() Sasha Levin <sasha.levin@oracle.com> - 2016-01-25 17:00 +0100
  Re: [PATCH] signals: work around random wakeups in sigsuspend() Oleg Nesterov <oleg@redhat.com> - 2016-01-25 20:10 +0100
    Re: [PATCH] signals: work around random wakeups in sigsuspend() Peter Zijlstra <peterz@infradead.org> - 2016-01-25 20:40 +0100
  Re: [PATCH] signals: work around random wakeups in sigsuspend() Andrew Morton <akpm@linux-foundation.org> - 2016-01-25 22:40 +0100
    Re: [PATCH] signals: work around random wakeups in sigsuspend() Oleg Nesterov <oleg@redhat.com> - 2016-01-26 22:20 +0100
      Re: [PATCH] signals: work around random wakeups in sigsuspend() Peter Zijlstra <peterz@infradead.org> - 2016-01-27 09:50 +0100
        Re: [PATCH] signals: work around random wakeups in sigsuspend() Oleg Nesterov <oleg@redhat.com> - 2016-01-27 17:50 +0100
          Re: [PATCH] signals: work around random wakeups in sigsuspend() Peter Zijlstra <peterz@infradead.org> - 2016-01-27 19:00 +0100
          Re: [PATCH] signals: work around random wakeups in sigsuspend() Andrew Morton <akpm@linux-foundation.org> - 2016-01-27 19:40 +0100
            Re: [PATCH] signals: work around random wakeups in sigsuspend() Oleg Nesterov <oleg@redhat.com> - 2016-01-27 22:10 +0100
        Re: [PATCH] signals: work around random wakeups in sigsuspend() Sasha Levin <sasha.levin@oracle.com> - 2016-01-27 18:30 +0100
  Re: [PATCH] signals: work around random wakeups in sigsuspend() Ingo Molnar <mingo@kernel.org> - 2016-01-26 07:50 +0100
    Re: [PATCH] signals: work around random wakeups in sigsuspend() Oleg Nesterov <oleg@redhat.com> - 2016-01-26 16:10 +0100

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